Switch power is usually used as a power supply for all types of electric equipment, to play a role of converting an unadjusted AC or DC input voltage into an adjusted AC or DC output voltage. Since the switch power needs to adapt to different working conditions, the performance requirements on the dynamic response of the power are higher and higher. Good dynamic effects require small voltage changes and the voltage recovery time. For example, in the application of home appliances, the power load of a washing machine changes quickly and greatly, so that overvoltage and undervoltage are introduced into the output voltage of the power, and when the overvoltage and undervoltage are too large, the load damage to the washing machine is relatively larger; in addition, in mobile phone charging, when a charger is standby and the mobile phone is loaded suddenly, the output voltage is reduced, and when the voltage is reduced under the normal voltage of a battery, there is a certain damage to the battery. Therefore, the dynamic performance needs to be increased.
In present power management, in order to enable the power to have higher efficiency, a multi-mode control method is selected in the power generally, but the multi-mode control method will cause the problem of decreasing the dynamic performance. A flyback converter of 5V and 1 A is taken as an example in the following; when the load power consumption is reduced, a switch frequency will be decreased usually so as to reduce the circuit losses. It is defined that load A is a 1 A load, the switch frequency fA is 70 kHz, and the circuit has higher efficiency. Load B is a 0.7 A load, and the switch frequency fB is 70 kHz. Load C is a 0.2 A load, and the switch frequency fC is 20 kHz. Load D is a 0.05 A load, and the switch frequency fD is 20 kHz. The switch frequency at the load point is selected according to the system efficiency requirements. When the load is between A and B, a PWM mode is adopted, when the load is between B and C, a PFM mode is adopted, when the load is between C and D, the PWM mode is adopted and is donated as a DPWM mode, when the load is less than the load D, the PWM mode is adopted and is donated as the DPFM mode, and the working modes of the loads from light to heavy are DPFM-DPWM-PFM-PWM. If the load is standby, according to the size of a dummy load, assuming that a standby frequency is 2 kHz, and the control mode at the moment is the DPFM mode; if the load is suddenly changed into full load, and the output voltage is decreased at a very quick speed, according to a supplementary result, a control mode will pass through the DPWM, PFM and PWM modes respectively; when the supplementary result does not reach the full load condition, the output voltage is continuously decreased, which may cause severe voltage drop that is unbearable in some cases; and similarly, when the full load is switched into a light load, an intermediate mode control process will cause the continuous increase of the voltage, and the voltage will have a great overshoot. Moreover, in some cases, in order to prevent the control mode from being repeatedly switched between two modes near a switching point during mode switching, it needs to go through several cycles to confirm the need to switch the mode control when switching from one mode to another mode; under such condition, the dynamic effect will be further reduced.
In addition, in some controls, the sampling can only be conducted once in one cycle. For example, in a flyback power with primary feedback, the output voltage can only be sampled before the secondary current drops to zero. In this way, when the load is switched from light to heavy, the switch frequency of the DPWM is low, and even if the PI adjustment is very large, the dynamic process is slower for stability.
Moreover, in order to accelerate the dynamic response speed, some control methods can increase PI parameters to accelerate the supplementation, so as to increase the dynamic effects, but the improvement to increase the dynamic performances under the multi-mode control is not great.
Therefore, due to the increasingly high dynamic performance requirements and the dynamic problems brought by the multi-mode control method, a control method for improving dynamic response of switch power is proposed. The control method has very good effects on decreasing the overshoot and undervoltage of the voltage and decreasing the dynamic recovery time, which is very necessary for increasing the dynamic performance of the circuit.